Method of recovering gasoline from gases



DeC l0, 1940- P. c. KEITH, JR., Erm. 2,224,227

METHOD OF RECOVERING GASOLINE FROM GASES .nlll

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I A ORNEY l INVENTO l// 6' /1/6/ RNW g IVI Patented Dec. 10, 1940 UNITEDSTATES PATENT OFFICE .METHOD F RECOVERING GASOLINE FROM GASESApplication April 23, 193s, serial No. 203,860

7 Claims.

Our invention relates to a method of recovering gasoline from gases.

Customary absorption systems used for recov-v ering gasoline from gasesare not efilcient when the gases which are to be subjected to absorptionare lean.

One object of our invention is to provide'aV method of recoveringgasoline from lean gases.

Another object of our invention is to provide an economical method ofrecovering gasoline and other liquid fractions from natural gasescontaining the same.

Other and further objects of our invention will appear from thefollowing description.

The accompanying drawing which forms part of the instant specificationand is to be read in conjunction therewith is a schematic view of oneform of apparatus capable of carrying out the method of our invention.

20 It has been suggested to use low temperature rectification for therecovery of gasoline from gases. We have found, however that when thisis attempted gas hydrates form, which clog the lines and prevent furtheroperation of the proc- 25 ess. In general, our invention contemplates.the dehydration of the gas before its reduction in temperature. 'Ihedehydration is conducted to such an extent that, at the temperaturesinvolved, gas hydrates will not form.

30 More particularly referring now to the drawing, a feed g-as ischarged through pipe I into a gas scrubber or knock-out drum 2. In atypical plant adapted to carry out the method of our invention, we havebeen able to recover 11,800 gallons of gasoline per day,. charging10,000,000 cubic feet of gas per day. The scrubbing liquid may be anydesirable liquid such as a slop crude, which is introduced into thescrubbing drum 2 through line 3, removed through 40 line 4, and pumpedby pump 5 to slop crude storage. through pipe 6 at atmospheric pressureand at a temperature of about 100 F. The gas from pipe 6 passes throughpipes 1 and 8 to compressors 9 45 and lll in which the gas is compressedto a pressure of about 75 pounds per square inch at which pressure thetemperature will be about 270 F. The gas leaves the compressors 9 and I0through pipes II and I2 and passes into pipe I3 into a 50 heat exchangerI4 into which cooling Water is introduced through pipe I5. The heatexchanger is such that the gas leaving the heat exchanger I4 throughpipe I6 will be at a temperature of about 100 F. This gas enters heat 55exchanger I1 in whichit is reduced in temper- The scrubbed gas leavesthe drum 2A ature by heat exchange with a chilled gaseous medium. Thischilled gas is withdrawn from vflash drum I8 through pipe I9 by which itis conducted to heat exchanger Il. The chilled gas is normally at atemperature in the vicinity of 5 p -30 F. The rate of flow of the feedgas is such with respect to the rate of flow of the cooling gas that thefeed gas leaving lthe heat exchanger I1 through pipe 20 will be at atemperature of l about 41 F. 'I'his temperature is sulcient to 10liquefy considerable Water and liquid fractions contained in the gas.'I'he cooled feed gas is introduced from pipe into a Water separatortank 2I from which water is withdrawn through pipe 22. At thetemperatures involved and for 15 the rate of feed given in a plantoperated according to our invention, about 1200 pounds of Water perhourwere withdrawn from the water separator drum 2l. About 200 gallons ofgasoline per hour were also precipitated. 'I'his gasoline 20 waswithdrawn from the separator 2| through pipe 23 and pumped by pump 24through pipe 25 for introduction into the stabilizer tower 26 via pipes2l and 28. The cooling gas introduced into the heat exchangerI'l'through pipe I9 is 25 Withdrawn from the heat exchanger through pipe2l and introduced into a manifold 28" from which it may be Withdrawnthrough pipes and 29 for use as fuel or discharged as tail gas throughpipe 3I. 1f desired, tail gas may be used 30 as a revivifying medium forthe driers 32 and 33 as will be hereinafter more fully pointed out. Thecooled gas, freed of precipitated Water and gasoline, is removed fromthe separator 2l through pipe 34 and passed to the drying step. 35 Thegas will be substantially at 4the same temperature in pipe 34A as whenit entered the separator, namely at about F. 'Ihe driers 32 and 33comprise chambersk35 and 36 adapted to be operated alternately. Thegas'from pipe 34 40 is introduced into the manifold 31. By opening thevalve 38 and closing valve 39, drier 32 will be the one in use. A bodyof an adsorptive medium 40, such as silica gel, serves to adsorbmoisture from the gas. The temperature of the gas entering the drier isabove that at which the gas hydrates will form. The drying is such thatthe gas may now be chilled to a much lower temperature, enabling therecovery of substantial amounts of gasoline from the gases beingsubjected to our process. The dried gases leave the drier 32 throughmanifold 4I and pass into pipe 42. When drier 32 is in use, valve 43will be open and valve 44 will be closed. After drier 32 has been in usefor a period, it becomes humidied and its dehydratingability decreases.When this point is reached, valves 38 and 43 are closed and valves 99and 44 are opened. Valve 45 is opened, permitting tail gases frommanifold 28 to pass through heat exchanger 46 in which the gases areheated by superheated steam introduced through pipe 41, lto atemperature of about 325 F. Valve 48 is closed and valve 49 is opened.The gases leaving the heat exchanger 46 through pipe 50 may pass throughthe chamber 35, heating the body of silica gel 40 and evaporatingmoisture therefrom. The drying gases that oo ntain moisture leave thedrier 32 through pipe 5I and valve 52 being open and valve 53 beingclosed, the gases will pass through pipe 54 to the 'tail gas manifold28. The heating of the gases expands them, causing them to flow throughpipe 54 into the manifold 28. It will be understood, of course, that thedrying gases may be directed to drier 33 by opening valve 48 and closingvalve 49 when drier 32 is in use.

The dehydrated gases from pipe 42 pass into a heat exchanger 55 wherethey are chilled to a very low temperature. The cooling medium for thechilling passes to a heat exchanger 55 through pipe 56 and may compriseliquid propane, withdrawn by pipe 56 from propane ash drum 51. Inchilling the gases in heat exchanger 55, some -of the propane will bevaporized. 'Ihe propane vapors leave the heat exchanger 55 through pipe58 and pass into the propane flash drum 51, whence they are removedthrough pipe 59 and pass to a compressor 60, whence they are compressedto about 240 pounds per square inch. The propane gas in pipe59 will beat a temperature of about 40 F. and at a pressure of about 13 pounds persquare inch. The propane leaving the compressor 60 through pipe 6| willbe at a temperature of about 135 F. The hot compressed propane is passedthrough a cooler 62 in heat exchange with a cooling medium such as waterintroduced through pipe 63 in which Ithe propane is cooled to atemperature of about F. The cooled propane leaves the heat exchanger 62through pipe 64 and passes into a propane receiver 65. The propane iswithdrawn from the receiver 65 through pipe 66 and passed to a heatexchanger 61. In the heat exchanger 61, the propane is cooled by heatexchange with unstabilized gasoline, introduced through pipe 68, beingwithdrawn by pump 69 from flash drum I8. The unstabilized gasolinepassing through the heat exchanger 61 is introduced thereto at atemperature of about 30 F. 'I'he propane leaves the heat exchanger 61through pipe 10 at a temperature of about 40 F. and is introduce intothe propane flash drum 51.

The gases leaving the heat exchanger 55 will be cooled to a temperatureof about 30 F. This low temperature will precipitate gasoline and lowboiling hydrocarbons. The condensed liquid and uncondensed 'gases arewithdrawn from the heat exchanger 55 through pipe 1I and are introducedinto the flash drum I 8. The gaseous hydrocarbons are withdrawn from theflash drum I8 through pipe I9 as heretofore described. The liquidcondensate is withdrawn from the flash drum I8 through pipe 12controlled by Valve 13 and pumped by pump 69 through heat exchanger 61as pointed out above.

In the example which is being used throughout this specification, thegasoline leaves the heat exchanger 61 through pipe 14 at a temperatureof about 90 F. In pipe 14, the gasoline is joined by the gasolineprecipitated in the separator 2| and the unstabilized gasoline passesinto heat exchanger 15 through pipe 21. In the heat exchanger, it isheated to a. temperature of about F. and at this temperature, it entersthe stabilizer 26 through pipe 28. The gasoline is reboiled instabilizer tower 26 in reboiler 16 which is supplied steam through pipe11. The bottom of the tower is kept at a temperature of about 222 F. andis operated under a pressure of 140 pounds per square inch. The vaporsleaving the top vof the stabilizer through pipe 18 are at a temperatureof about F. They pass through a heat exchanger 19, supplied with acooling medium through pipe 80 and are cooled therein -to a temperatureof about 100 F. The condensate passes from heat exchanger 19 throughpipe 8I into a refiux drum 82 from which reux is withdrawn through pipe83 and pumped by pump'84 through pipe 85 to the tower as a controlreiiux, keeping the top tower at about 100 F. Stabilizer gas is ventedthrough pressure control valve 86 bypipe 81. The stabilizer gas maybepassed to the tail gas manifold 28. The stabilized gasoline is withdrawnfrom the stabilizer tower 26 through pipe 88 and passes through heatexchanger 15, being withdrawn therefrom through pipe 89 and passing tostorage tanks 90 and 9I whence it is withdrawn through manifold 92. Thestabilized gasoline leaving the heat exchanger 15 wiil be atatemperature of about 100 F.

It is to be understood that the temperatures and pressures usedthroughout this specification are by way of illustration only and not byway of limitation.

It will be seen that we have accomplished the objects of our invention.We have provided a method of recovering gasoline from lean gases by lowtemperature rectification and stabilization while avoiding the formationof gas hydrates. The use of lean tail gas to revivify the driers and thedrying of the precooled tail gas before final chilling to prevent theformation of gas hydrates are novel features, enabling the employment ofour invention to recover valuable low boiling liquid hydrocarbonssuitable for use as a motor fuel from lean hydrocarbon gases. Therecovery of the valuable liquid hydrocarbons by means-of our methodcould not be accomplished by conventional absorption or rectificationmethods.

It will be understood that certain features and subcombinations are ofutility and may be ernployed without reference to other features andsub-combinations. This is contemplated by and is within the scope of ourclaims. obvious that various changes may be made in details within thescope of our claims without departing from the 'spirit of our invention.It is, therefore, to be understood that our invention is not to belimited to the specific details shown and described.

Having thus describedour invention, we claim:

1. A method of recovering gasoline from mixtures of hydrocarbon gaseswhich comprises compressing hydrocarbon gases, cooling the compressedgases to a relatively low temperature above the freezing point of waterand above that at which solid hydrocarbon hydrates will form to condensewater and some gasoline, separating the water from the remaining gasesand separating the gasoline from the remaining gases, passing theremaining gases through a dryer zone to remove substantially all themoisture from such gases, then reducing the temperature of the re- It isfurther maining dried gases to a relatively low temperature below thefreezing point of water to condense gasoline, combining the gasolineseparated in the two cooling stepsand introducing it into.

a stabilizing zone for stabilizing the gasoline.

2. A method of recovering gasoline from mixtures of hydrocarbon gaseswhich comprises compressing hydrocarbon gases, cooling the compressedgases to a relatively low temperature above the freezing point of waterand above that at which solid hydrocarbon hydrates will form to condensewater and some gasoline, separating the water from the remaining gasesand separating the gasoline from the remaining gases, passing theremaining gases through an adsorbing agent in a dryer zone to removesubstantially all the moisture from such gases, then reducing thetemperature of the remaining dried gases to a relatively low temperaturebelow the freezing point of water to condense gasoline, passing thecooled gases and gasoline to a separating zone to separate gasoline fromcold gases and using the separated cold gases for initially cooling thecompressed gas at the beginning of the method and thereafter heating theseparated gases and using the heated gases as a drying medium forrevivifying the adsorbing agent in another dryer zone.

3. A method of recovering liquid hydrocarbons within the gasolineboiling range from mixtures of hydrocarbon gases containing gasolineconstituents which comprises cooling said hydrocarbon gases undersuperatmospheric pressure to a relatively low temperature above thefreezing point of water and above that at which solid hydrocarbonhydrates will form to condense water and some gasoline,.separatingWater, liquid hydrocarbons containing gasoline constitutents andremaining gases from each other, passing gases thus separated through adryer zone at atemperature above that at which solid hydrocarbonhydrates will form to remove substantially all of the moisture from suchgases. reducing the tem perature of the thus dried gases to a relativelylow temperature below the freezing point of water to condense liquidhydrocarbons containing gasoline constituents and stabilizing gasolineseparated in the two cooling steps.

4. A method of recovering liquid hydrocarbons within the gasolineboiling range from mixtures of hydrocarbon -gases containing gasolineconstituents which comprises cooling said hydrocarbon gases undersuperatmospheric pressure to a relatively low temperature above thefreezing point of water and above that at which solid hydrocarbonhydrates will form to condense Water and some gasoline, separatingwater, liquid hydrocarbons containing gasoline constituents andremaining gases from each other, passing gases thus separated through adryer zone at a temperature above that at which solid hydrocarbonhydrates will form to remove substantially all of the moisture from suchgases, reducing the temperature of the thus dried gases to a relatively10W temperature below the freezing point of water to condense liquidhydrocarbons containing gasoline constituents, combining gasolineconstituents separated in the two cooling steps and introducing combinedconstituents into an enlarged zone wherein volatile constituents areremoved.

5. A method of recovering liquid hydrocarbons within the gasolineboiling range from mixtures of hydrocarbon gases containing gasolineconstituents which comprises cooling said hydrocarbon gases undersuperatmospheric pressure to a relatively low temperature above thefreezing point of water and above that at which solid hydrocarbonhydrates will form to condense water and some gasoline, separatingwater, liquid hydrocarbons containing gasoline constituents andremaining gases from each other. passing gases thus separated through adryer zone at a temperature above that at which solid hydrocarbonhydrates will form to remove substantially all of the moisture from suchgases, reducing the temperature of the thus dried gases to a relativelylow temperature below the freezing point of water to condense liquidhydrocarbons containing gasoline constituents, separating liquidhydrocarbons containing gasoline constituents from cold gases andutilizing separated cold gases thus obtained for initially cooling thehydrocarbon gases under superatmospheric pressure.

6. A method of recovering liquid hydrocarbons within the gasolineboiling range from mixtures of hydrocarbon gases containing gasolineconstituents which comprises cooling said hydrocarbon gases undersuperatmospheric pressure to a relatively low temperature above thefreezing point of water and above that at which solid hydrocarbonhydrates will form to condense water and some gasoline, separatingwater, liquid hydrocarbons containing gasoline constituents andremaining gases from each other, passing gases thus separated/through adryer zone at a temperature above that at which solid hydrocarbonhydrates will form to remove substantially all of the moisture from suchgases, reducing the temperature of the thus dried gases to a relativelylow temperature below the freezing point of water to condense liquidhydrocarbons containing gasoline constituents, separating liquidhydrocarbons containing gasoline constituents 4from cold gases, heatingcold gases thus obtained and using the heated gases as a drying mediumfor revivifying the absorbing agent in another dryer zone.

'1. A method of recovering gasoline from mix- .tures of hydrocarbongases which comprises cooling hydrocarbon gases under superatmosphericpressure to a relatively low temperature above the freezing point ofwater and above that at which solid hydrocarbon hydrates will form tocondense water and some gasoline. separating the water from theremaining gases and separating the gasoline from the remaining gases,passing the remaining gases through a dryer zone at a temperature abovethat at which solid hydrocarbon hydrates will form to removesubstantially all of the moisture from such gases. then reducing thetemperature of the remaining dried gases to a relatively low temperaturebelow the freezing point of water to condense gasoline, combining thegasoline separated in the two cooling steps and introducing it into astabilizing zone for

